diff --git a/packages/backend/src/core/NoteCreateService.ts b/packages/backend/src/core/NoteCreateService.ts
index b2c8fd2bd3..497328eb38 100644
--- a/packages/backend/src/core/NoteCreateService.ts
+++ b/packages/backend/src/core/NoteCreateService.ts
@@ -436,6 +436,16 @@ export class NoteCreateService implements OnApplicationShutdown {
 			mentionedUsers = data.apMentions ?? await this.extractMentionedUsers(user, combinedTokens);
 		}
 
+		const willCauseNotification = mentionedUsers.filter(u => u.host === null).length > 0 || data.reply?.userHost === null || data.renote?.userHost === null;
+
+		if (process.env.MISSKEY_BLOCK_MENTIONS_FROM_UNFAMILIAR_REMOTE_USERS === 'true' && user.host !== null && willCauseNotification) {
+			const userEntity = await this.usersRepository.findOneBy({ id: user.id });
+			if ((userEntity?.followersCount ?? 0) === 0) {
+				this.logger.error('Request rejected because user has no local followers', { user: user.id, note: data });
+				throw new IdentifiableError('e11b3a16-f543-4885-8eb1-66cad131dbfd', 'Notes including mentions, replies, or renotes from remote users are not allowed until user has at least one local follower.');
+			}
+		}
+
 		tags = tags.filter(tag => Array.from(tag).length <= 128).splice(0, 32);
 
 		if (data.reply && (user.id !== data.reply.userId) && !mentionedUsers.some(u => u.id === data.reply!.userId)) {